Marvin:
The starting fill was at 2100# by the Hill Pump guage and that put the gun slightly into the yellow fill pressure area of the gun guage, above the green area.
Shooting down to 2000# brought the gun guage pressure to about the top of the green area; that woud be shot #9/10. Shot #12 is where I hit the first black line in the Green area of the gun pressure quage.
Now, on the chart, the shots highlighted in green area on the chart start at shot 20 and that pressure was 1700#.
From this I concluded that my optimal fill without mod would be 1700# (Hill Pump Guage) and I would get about 20 good shots. The max spread in the Green shot area of the chart equates to about a 0.4 inch change in drop position of the pellet at 35 yards. By drop position I mean if you shot strait out (bore site) at the high velocity, then from the same position at the low velocity, I calculated the second shot would be about 0.4 inches lower - basically, at 35 yards, you should not expect any better than 0.5 inch groups in the optimal pressure area of the un-tuned gun - more like 1-inch groups when you factor in hold, breezes, scope adjustment, and on and on ;.) So far the best I can do is 1.5 inch groups at 35 yards from a sand bag rest.
Scott